1. Field of the Invention
This invention relates to hydrodehalogenation catalysts and their use for the catalytic hydrogenolysis of fluorohalocarbons or fluorohalohydrocarbons and more particularly to carbon supported metal catalysts containing gold and their use in the hydrogenolysis of fluorohalocarbons or fluorohalohydrocarbons.
2. Background
A number of chlorinated fluorocarbons are considered to be detrimental toward the Earth's ozone layer. There is a world-wide effort to develop materials that can serve as effective replacements. For example, 1,1,1,2-tetrafluoroethane (HFC-134a), a hydrofluorocarbon containing no chlorine, is being considered as a replacement for dichlorodifluoromethane (CFC-12) in refrigeration systems because of its zero ozone depletion potential. There is thus a need for manufacturing processes that provide fluorocarbons that contain less chlorine.
One method of reducing the chlorine content of halogen substituted hydrocarbons containing chlorine as well as fluorine is reacting organic starting materials containing chlorine and fluorine with hydrogen at elevated temperature in the presence of a hydrogenation catalyst (e.g., supported Group VII or Group VIII metal catalysts). British Patent Specification 1,578,933 discloses, for example, that HFC-134a can be prepared by the hydrogenolysis of 2,2-dichloro-1,1,1,2-tetrafluoroethane (CFC-114a) or 1,1,1,2-tetrafluorochloroethane (HCFC-124) over palladium on carbon or palladium on alumina hydrogenation catalysts. There remains a continued interest in providing improved hydrogenolysis processes for the manufacture of HFC-134a as well as other fluorohydrocarbons and fluorohalohydrocarbons.
Techniques for enhancing the durability of Group VIII metal hydrogenolysis catalysts have been disclosed. The catalyst improvements described in Eur. Pat. Appln. 347,830 and Jap. Pat. Appln. 1-128,942 are achieved by the addition of other elements, such as Group IB (e.g., gold), lanthanum, lanthanide elements, and rhenium to the Group VIII metal catalysts. The additives are said to prevent sintering and also increase the durability and the mechanical strength of the catalysts. In general, the mixed metal catalysts are dried at 500.degree. C. to 550.degree. C. and are then reduced (e.g., with hydrogen).